890 g of copper is mixed with 100 g of zinc to form brass. The density of copper is 8.9 g/cm³ and the density of zinc is 7.1 g / cm ³ . a ) What is the volume of copper and zinc used to make the brass ?
b ) Calculate the density of the brass .

Density ρ is equal to mass m per unit volume v, or

ρ = m / v

Solve for volume:

v = m / ρ

(a) 890 g of copper, which has a density of 8.9 g/cm³, has a volume of

v = (890 g) / (8.9 g/cm³) = 100 cm³

100 g of zinc, with density 7.1 g/cm³, has a volume of

v = (100 g) / (7.1 g/cm³) ≈ 14.08 cm³

(b) The density of brass is then

ρ = (890 g + 100 g) / (100 cm³ + 14.08 cm³) ≈ 8.68 g/cm³

i can't see the picture : /

2. angles qrt and qst both measures 156 degrees.

step-by-step explanation:  

we have been given a diagram of a circle and we are told that measure of arc qvt is 156 degrees.  

we can see from our given diagram that angle qrt and angle qst subtends to arc qvt.

since we know that angles subtended by the same arc at the circumference are always equal.

by angle subtended by same arc theorem, measure of angle qrt and angle qst will be equal to the measure of arc qvt.

therefore, angles qrt and qst both measures 156 degrees and 2nd statement is the correct choice.